1. Field of the Invention
The present invention generally relates to power switching circuits and, more particularly, to those circuits used to disconnect power from an appliance following the expiration of predetermined interval of disuse.
2. Prior Art
With the increased need to conserve energy and to eliminate the unwarranted expenditures arising out of damage to equipment from applying power thereto during periods of disuse, it has become evident that means are necessary to improve present procedures and apparatus. The prior art discloses a number of devices which are used to switch or otherwise apply power to and remove power from electrical appliances such as electric typewriters. In substantially all of the devices disclosed by the prior art, the means used to switch power to and from the apparatus employs either mechanical, electromechanical or thermal elements. One of the devices disclosed by the prior art is specifically incorporated into a typewriter. A thermal cut-out switch is used for controlling the power delivered to a driving motor of the electric typewriter. A heater comprising a coil of resistant wire heats a bimetallic member causing it to bow in a specified direction. When the operator of the typewriter turns power to the on position, the heater will be periodically impulsed with current with the result that it will cause the bimetallic member to bow in the predetermined direction. Therefore, as long as the operator is using the machine, the heater will be kept hot enough to prevent the bimetallic member from being deflected in the opposite direction and thereby causing the motor to be disconnected from the circuit. Once the operator leaves the machine unattended, the heater will cool thereby disconnecting the power to the typewriter.
A mechanical cut-off device described by the prior art is pivotally supported on a typewriter for engagement with a continuously driven power roll. A driving wheel, an operating cam and a climbing wheel are coaxially mounted in a bracket for engagement with the continuously operated power roll. If the machine is left unattended for a predetermined period, the climbing wheel will frictionally engage the operating cam which will act to cut off the power to the electric motor. The climbing wheel is resettable to its quiescent position upon operation of selected ones of the functioning elements of the typewriter.
All of the devices disclosed by the prior art have a number of inherent difficulties which are common irrespective of whether the devices utilize mechanical, electromechanical or thermal principles for their operation. In all cases, the devices are integrally coupled to the specific machine with which they are used, and in all cases described, the switching or cut-off device is used with a typewriter. Although the present invention is preferably utilized with a typewriter, it is clear that the present invention can be used with any appliance or machine which utilizes intermittent operator contact.
The present invention employs an electrically conductive antenna which receives an input signal derived from the energy radiated from alternating current machinery within the vicinity of the appliance. When the operator touches the input antenna, the ambient electrical signal is applied to the input of the present invention circuit. The input signal is shaped into electrical signals which can be used to trigger a timing element. An alternating current switch controls the delivery of power to the typewriter or other suitable appliance. So long as the operator makes contact with the input antenna, the timing elements will continue to be reset thereby reinitiating any time-out sequence thereof. After the operator discontinues use of the machine to which the present invention is coupled, the timing element will continue to provide an electrical signal responsive to its status, the signal preventing the alternating current switch from disconnecting the power to the machine. After the time-out of a predetermined interval, the alternating current switch will be shut off and power will be removed from the machine. In order to restart the appliance, the operator need merely make contact with the input antenna which will result in activation of the alternating current switch and thereby restore power to the typewriter or other appliance being utilized.